Poly(arylene sulfide/sulfone) polymers are thermoplastic polymers of interest for film, fiber, molding, and composite applications because of their high glass transition points and good mechanical and electrical properties and chemical resistance.
Poly(arylene sulfide/sulfone) polymers can generally be prepared by the reaction of a polyhalo aromatic sulfone with an alkali metal sulfide and a polar organic compound, as disclosed in U.S. Pat. No. 4,127,713 and U.S. Pat. No. 4,808,698.
One problem experienced with poly(arylene sulfide/sulfone) polymers in the past is that they exhibited relatively low melt stability. U.S. Pat. No. 4,774,276 discloses a method to produce poly(arylene sulfide/sulfone) polymers having increased melt stability by treating the poly(arylene sulfide/sulfone) polymers with a zinc source, thereby incorporating zinc cat ions into the polymer.
For certain poly(arylene sulfide/sulfone) polymer applications, such as the molding of injection molded parts for example, it is desired that the polymer exhibit a high degree of clarity. In order for the polymer to exhibit a high degree of clarity, the polymer should be relatively free of impurities such as salt by-products and metal ions. It can therefore be seen, that the process of increasing the thermal stability of the poly(arylene sulfide/sulfone) polymer could result in introducing impurities into the polymer which affect the clarity of molded parts. It would therefore be desirable to increase the thermal stability of a poly(arylene sulfide/sulfone) polymer while not adversely affecting its purity.
For certain other applications which employ poly(arylene sulfide/sulfone) polymers, such as the production of composites, it is also desirable to have a polymer of increased purity in order to aid in the interfacial bonding of the resin and fiber used in the composite. Again, impurities in the polymer interfere with the resin/fiber interfacial bonding and are therefore undesirable, Since the thermal stability of the polymer in the composite is important also, it would be desirable to have a method of increasing the thermal stability of a poly(arylene sulfide/sulfone) polymer while not adversely affecting the purity of the polymer.
It is therefore an object of this invention to provide a process for preparing a poly(arylene sulfide/sulfone) polymer having increased melt stability. It is further an object of this invention to provide a poly(arylene sulfide/sulfone) polymer which is relatively free from impurities and is thus useful in the preparation of injection molded parts exhibiting a high degree of clarity and composites having a good resin/fiber interface.